Technical Field
The present disclosure relates to an elastic cap detachably mounted to the tip portion of a barrel from which a puncture needle projects and a syringe assembly with the elastic cap.
Background Art
For example, as shown in U.S. Pat. No. 6,719,732, a prefilled syringe in which a drug or the like is pre-filled is provided with an elastic cap detachably mounted to the tip portion of a barrel having a puncture needle, thereby protecting the puncture needle and sealing the needle hole of the puncture needle.
The elastic cap is attached before a plunger is inserted into the interior space of the barrel and before the barrel is filled with a drug or the like. The process of attaching the elastic cap to the barrel in accordance with the prior art is described below with reference to FIGS. 4 and 5.
As shown in FIG. 4, an elastic cap 1 in accordance with the prior art is provided with a bottomed cylindrical shape having an open end portion 2 at one end and a thick bottom wall 3 at the other end and has a receiving hole 4 extending from the open end portion 2 toward the bottom wall 3 therein. The receiving hole 4 receives an annular head 7 of a barrel tip portion 6 provided at the end of a barrel 5 and a puncture needle 8 extending from the end of the barrel tip portion 6.
Specifically, the receiving hole 4 is provided with a large diameter portion 4a, an intermediate diameter portion 4b, and a small diameter portion 4c in that order from the open end portion 2 toward the bottom wall 3. The inner diameter of the large diameter portion 4a is larger than the outer diameter of the annular head 7 formed in the barrel tip portion 6, and the inner diameter of the intermediate diameter portion 4b is substantially equal to the outer diameter of the annular head 7. The small diameter portion 4c is reduced in diameter in a substantially tapered shape from an end of the intermediate diameter portion 4b toward the bottom wall 3 so that the small diameter portion 4c continuously changes from an inner diameter substantially equal to the inner diameter of the intermediate diameter portion 4b to an inner diameter substantially equal to the outer diameter of the puncture needle 8.
When the puncture needle 8 and the barrel tip portion 6 are inserted into the receiving hole 4 as shown in FIG. 5, the puncture needle 8 and the barrel tip portion 6 are moved from the open end portion 2 toward the bottom wall 3 so that the axis of the puncture needle 8 is axially aligned with an axis A of the receiving hole 4 and an insertion direction B of the puncture needle 8 is aligned with the axis A. This allows the tip of the puncture needle 8 to reach a base end surface 3a of the bottom wall 3 through the large diameter portion 4a, the intermediate diameter portion 4b, and the small diameter portion 4c. Thereafter, the puncture needle 8 and the barrel tip portion 6 are further moved as described above, thus inserting the tip of the puncture needle 8 from the base end surface 3a into the bottom wall 3 and sealing the needle hole of the puncture needle 8.
In this regard, the annular head 7 is press-fit into the intermediate diameter portion 4b against the elastic force of the elastic cap 1. Thus, the force (elastic force) by which the increased intermediate diameter portion 4b attempts to return to its original diameter acts on the annular head 7 so that the elastic cap 1 is positioned relative to the tip portion 6 of the barrel 5.
As described above, the elastic cap 1 is detachably mounted to the tip portion 6 of the barrel 5 so as to seal the needle hole of the puncture needle 8 so that a syringe assembly 9 is available. This enables a space between the interior space formed in the barrel 5 and the plunger (not shown) slidably received in the interior space to be filled with a liquid such as a drug in a liquid-tight manner. As described above, the receiving hole 4 has the large diameter portion 4a, the intermediate diameter portion 4b, and the small diameter portion 4c, each having a different inner diameter, where the tip diameter of the small diameter portion 4c having a minimum inner diameter thereof is substantially equal to the outer diameter of the puncture needle 8. As such, there is a concern that inserting the tip of the puncture needle 8 from the base end surface 3a into the bottom wall 3 may become difficult if the axis of the puncture needle 8 is slightly misaligned away from the axis A of the receiving hole 4 or if the insertion direction B is slightly inclined relative to the axis A, upon insertion of the puncture needle 8 and the barrel tip portion 6 into an insertion hole 4.
That is, if the insertion position of the puncture needle 8 is misaligned or the insertion direction B is inclined, it is contemplated that the tip of the puncture needle 8 may be inserted into the side wall of the receiving hole 4 before the tip of the puncture needle 8 reaches the base end surface 3a of the bottom wall 3. In particular, since the small diameter portion 4c is tapered, the puncture needle 8 is likely to be inserted into the side wall of the receiving hole 4. The thickness of the receiving hole 4 is thinner than that of the bottom wall 3. Thus, there is a concern that ensuring an insertion length capable of fully sealing a needle hole may become difficult if the puncture needle 8 is inserted into the side wall of the receiving hole 4.
Furthermore, the end surface of the puncture needle 8 is generally provided with an edge inclined relative to the axis of the puncture needle 8. When such a tip of the puncture needle 8 moves into an elastic member constituting the elastic cap 1, the moving direction thereof is likely to be oriented along the slope of the edge. If the puncture needle 8 is inserted into the side wall of the receiving hole 4, the puncture needle 8 moves in a direction away from the central axis of the elastic cap 1. In this regard, since the elastic cap 1 is less rigid than the puncture needle 8, a tip of the elastic cap 1 is bent opposite to the moving direction of the puncture needle 8 from the central axis of the elastic cap 1, as shown in FIG. 6. When the syringe assembly 9, to which the elastic cap 1 is attached in such a bent condition, is transferred to and from a container accommodating the syringe assembly 9, the tip of the elastic cap 1 may catch the container and this may result in poor yield and a damage of the puncture needle 8.
If the puncture needle 8 is inserted into the thin side wall of the receiving hole 4 as described above, the tip of the puncture needle 8 may eventually penetrate the side wall and be exposed to the outside of the elastic cap 1, as shown in FIG. 7. Moreover, as shown in FIG. 8, if a cover 1a having high rigidity compared to the puncture needle 8 etc. is attached to the outside of the elastic cap 1, the puncture needle 8 inserted into the side wall of the receiving hole 4 may be bent as it moves.
Furthermore, as described above, the elastic cap 1 is positioned in the syringe assembly 9 by press-fitting the annular head 7 into the intermediate diameter portion 4b having an inner diameter substantially equal to the annular head 7. Thus, it is difficult to accurately define a final insertion position of the barrel tip portion 6 relative to the receiving hole 4. Accordingly, there are concerns that an insertion length of the puncture needle 8 into the bottom wall 3 is insufficient and full sealing of the needle hole may become difficult, for example, if an insertion length of the puncture needle 8 and the barrel tip portion 6 into the receiving hole 4 is short. On the other hand, there are concerns that the puncture needle 8 is inserted into the bottom wall 3 more than necessary and silicone or the like applied to the surface of the puncture needle 6 to improve its lubricity may be removed if the insertion length is long.
That is, there are concerns in the above-described elastic cap 1 that it may become difficult to sufficiently protect the puncture needle 8 and the barrel tip portion 6 and to fully seal the needle hole without damaging the surface of the puncture needle 8 by accurately receiving the puncture needle 8 and the barrel tip portion 6 in the receiving hole 4. There is also a concern that it may become difficult to handle the syringe assembly 9 with the elastic cap 1 attached to the barrel tip portion 6.